M-type backward wave oscillator



Nov. 7, 1961 P. VlAL M-TYPE BACKWARD WAVE OSCILLATOR Filed Jan. 10, 1958 suoaf PuLsE Fig.5

United States Patent 3,008,093 M-TYPE BACKWARD WAVE OSCILLATOR Pierre Vial, Paris, France, assignor to Compagnie Generale de Telegraphic sans Fil, Paris, France Filed Jan. 10, 1958, Ser. No. 708,235 Claims priority, application France Jan. 24, 1957 Claims. (Cl. 331-82) Various travelling wave amplifier or oscillator tubes are known in the prior art. Among these are found travelling wave tubes having a rectilinear structure, a circular structure or a coaxial structure, with crossed electric and magnetic fields and generally designated as M-type tubes, and normally provided with an emissive cathode electrically separated from the electrode thereof which is without delay characteristics and which is generally designated as sole. Tubes of the type described hereinabove are also known in the prior art which are operated as pulsed systems by the application of pulses either to the cathode or to the auxiliary electrode facing the cathode and electrically separated from the electrode having delay characteristics and forming the anode of the tube.

The present invention relates to backward wave oscillators of the aforementioned type, and more particularly to an M-type backward wave oscillator which is pulsed in the operation thereof and which assures an output of pulsed oscillations having an essentially constant single frequency determined by the voltage of the applied pulses without producing a band of undesired frequencies.

The present invention has as its object such a pulsed oscillator of which the spectrum of frequency produced during the application of pulses is practically reduced to a single frequency and which offers simultaneously a good voltage Withstand ability, that is, which upholds the voltage between the anode and the sole without arcing in the tube.

It is already known in the prior art to combine the pulsed unblocking of the beam, obtained by one of the aforementioned means, with the simultaneous application to the sole of either a DC. voltage as described in US. Patents 2,702,370 and 2,704,350 to A. Lerbs, or with the simultaneous application of an alternating non-pulsed voltage of which the peaks are synchronized with the unblocking pulses, as it has been described in the copending application, Serial No. 488,752, now Patent No. 2,833,95 6, filed February 17, 1955, by D. Reverdin, and assigned to the assignee of the present application.

If the teachings of these prior art devices described hereinabove are applied to backward wave oscillators, it has been discovered that in the first case in which a DC. voltage is applied to the sole the frequency produced by the oscillator is a single frequency, but the high-voltage withstand ability of the tube is relatively poor and the dangers of arcing within the tube are relatively great.

It is to improve and obviate this last-mentioned inconvenience and disadvantage of the danger of arcing that the aforementioned copending application has suggested the second alternative, namely, the application to the sole of a nonpulsed alternating voltage. It has been found in connection with such an arrangement that the high-voltage withstand ability becomes effectively improved but that, if such an arrangement and system is applied to backward wave oscillators, the spectrum of frequencies produced is deteriorated, that is, that the oscillator produces simultaneously a large number of frequencies distributed over a considerable band instead of only the single frequency.

The present invention has as its object to eliminate this last-mentioned disadvantage of the generation of a large number of frequencies and to re-establish essentially the spectrum reduced to a single frequency obtainable with the first case while at the same time preserving 3,008,093 Patented Nov. 7, 1961 the advantages of good high-voltage withstand ability of the second alternative.

In contrast to the aforementioned copending application, which is based on combining the unblocking of the beam with the application to the sole of an alternating, non-pulsed periodic voltage, the present invention essentially consists in a combination of the pulsed unblocking of the electron beam with the application to the sole of a pulsed rectangular periodic voltage of which the duration of the pulse is essentially longer than that of the electron beam unblocking pulse but essentially shorter than the interval between two successive pulses applied to the sole, and of which the repetition frequency is the same as that of the beam unblocking pulses, of which each is positioned approximately near the center of the pulses applied to the sole.

Accordingly, it is an object of the present invention to provide a backward oscillator which combines a good high-voltage withstand ability together with an output limited essentially to only a predetermined single frequency.

It is another object of the present invention to provide a backward wave oscillator of the M-type in which pulses are both used to unblock the beam of electrons emitted by the cathode and to produce the electric field without, however, thereby increasing the risk of arcing within the tube or of producing more than essentially one predetermined frequency.

A still further object of the present invention is to provide a backward wave oscillator which olfers excellent high-voltage characteristics, i.e., in which relatively high voltages may be applied to certain electrodes without danger of arcing.

Still a further object of the present invention resides in the provision of a travelling wave tube constituting a backward wave oscillator of the M type in which certain electrodes are pulsed by the application of predetermined pulses and which produces only a single frequency preselected by the voltage of the pulse applied to at least one of the elements of the tube.

Another object of the present invention is to provide a system which applies pulses for unblocking the beam and for producing the electric field in predetermined timed relationship so as to produce the desired results mentioned hereinabove.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, two embodiments in accordance with the present invention, and wherein:

FIGURE 1 is a schematic diagrammatic view of the connection of a first embodiment of an M type backward wave oscillator operated by pulses.

FIGURE 2 is a schematic diagrammatic View of the connections of a second embodiment of an M-type backward wave oscillator operated by pulses, and

FIGURE 3 is a diagram indicating the shape and timed relationship of the applied pulses.

Referring now to the drawing, wherein like reference numerals are used through out the various views to designate like parts, and more particularly to FIGURE 1, reference numeral 1 generally designates a backward wave oscillator of the M-type of which the details of construction are known, per se. FIGURE 1 shows schematically the principal electrodes of the tube, namely, a filament 12, an emissive cathode 13, a sole 14 electrically separated or insulated from the cathode 13, an auxiliary electrode 15 facing the cathode 13 and controlling the electron beam, a delay line '16 forming the principal anode, and a collector 17. The tube 1 is provided with conductors or connections 2 and 3 fOr supplying electrical energy to the filament 12 and to the cathode 13, respectively. An electrical connection or conductor 4 is connected with the auxiliary electrode 15, while the connection or condoctor 5 is connected with the sole 14. The delay line 16 and the collector 17 are connected to the metallic envelope 18 of the tube which is effectively connected to ground. The electron beam of the tube 1 is unblocked by the application of relatively short pulses derived from the pulse source 6 by the intermediary of a transformer 7 the secondary winding of which is connected between the conductor 3 and ground, thereby applying such pulses between the cathode 13 and the delay line 16. In that case, the unblocking pulses must have a negative polarity.

In the embodiment of FIGURE 2 in which again similar tube elements (not shown) are provided with the M- type circular travelling wave tube 1, the only difference from the embodiment according to FIGURE 1 lies in the fact that the secondary winding of transformer 7 is connected between the conductors 3 and 4, i.e., between the cathode ,13 and the auxiliary anode 15. In that case, the pulses must be of positive polarity.

Without taking into consideration the sign of the pulses, i.e., whether they are negative or positive depending on the connection in accordance with either FIGURE 1 or FIGURE 2, such beam unblocking pulses are shown in FIGURE 3 in which they are designated by reference numeral 8, the duration of each of such pulse being shown by 7'2 and the repetition frequency by 1, whereby the period thereof is According to the present invention, the pulsed unblocking of the beam is combined with the simultaneous application between the envelope or ground and the conductor 5, that is, between the delay line 16 and the sole 14 of the oscillator, of negative pulses provided by the pulse source 9. The pulses 10 are essentially longer than the pulses 8 and enclose the same with the leading and trailing edges thereof in such a manner that each pulse 8 is positioned approximately in the center of a corresponding pulse 10. The long pulses are designated by reference numeral 10 in FIGURE 3 and are shown to have a dura tion 1- For example, the value of 1- may be taken as being equal to three to four times that of T2. In order to realize in practice the particular positioning of pulses 8 approximately in the center of the pulses 10, it is necessary that the time t between the leading edges of each pair of pulses 10 and 8 be approximately equal to The sources 9 and 6 are synchronized in such a manner that each pulse from the source 6 is triggered off by the leading edge of the pulse from the source 9, after being subjected to a delay I in a delay line or suitable delay means 11 interposed between the sources 9 and 6. Since such arrangements of such triggering devices are well known in the art, and form no part of the present invention, it is believed that a showing thereof may be dispensed with herein. As examples of synchronized triggered devices may be mentioned the various types of multi-vibrators and pulse shaping devices or the like, as used in connection with radar devices in which delayed pulses are produced for various purposes.

Since the synchronization described hereinabove assures the same repetition rate or frequency f for both the pulses 8 and 10, the repetition frequency is chosen as a function of the duration of T1 which is maintained as short as possible in itself while at the same time being relatively long with respect to the duration T in such a manner that the duration 1- remains still very considerably smaller to the interval The particular choice of values for 7- and f are largely dictated by a compromise between the condition of good frequency spectrum and that of good high-voltage withstandability.

It is thus seen that in the operation of a backward wave oscillator of the type described hereinabove, the electric field between sole and delay line is established prior to unblocking the beam of electrons. Since pulses are used for the control in accordance with the present invention which have a relatively steep leading edge, the electric field has assumed an already essentially constant value when the beam is unblocked by the application of the pulse 8. Since the frequency of oscillations produced by the oscillator is also a function of the value of the electric field, the frequency of oscillations may be limited to a single frequency provided the electric field has reach an essentially steady state condition, so to speak of, during the period when the electron beam is permitted to pass through the crossed electric and magnetic fields by the unblocking action of pulse 8. In order to limit the frequencies produced by the oscillator to a single frequency, it is also desirable to provide as steep as possible a leading and trailing edge for the pulses 8 and 10, particularly for the pulses 8.

For that reason, rectangular pulses or pulses as nearly rectangular as possible are desired. Such pulses may be obtained by any suitable means, well known in the art which enable the obtainment of essentially rectangular pulses.

While I have shown and described two embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of many changes and modifications within the spirit of the present invention.

Thus, any suitable synchronization device may be used to synchronize the pulses, either electrical or mechanical. Moreover, the sources for producing the pulses may be of any suitable type, either electronic, electric or mechanical. Furthermore, any suitable means may be provided to vary the absolute value on pulses 10 to thereby electrically tune the oscillator to a predetermined frequency, for example, a calibrated voltage divider, potentiometer or the like.

It is, therefore, obvious that the present invention is susceptible of many changes and modifications within the spirit and scope of the present invention, and I intend to cover all such changes and modifications as encompassed by the appended claims.

I claim:

1. An M-type backward wave oscillator arrangement having an emissive cathode, an auxiliary anode facing said cathode, a main anode and a sole electrode electrically separated from said cathode, comprising a first connection to said cathode, a second connection to said auxiliary anode, a third connection to said main anode, and a fourth connection to said sole electrode, means for applying relatively short periodic voltage pulses between said first connection and one of said second and third connections, and means for applying relatively long periodic voltage pulses between said third and fourth connections, the repetition rate of said short and long pulses being equal.

2. An arrangement as claimed in claim 1, further comprising means for positioning each of said short pulses. substantially symmetrically about the middle of a respective one of said long pulses.

3. An arrangement as claimed in claim 1, wherein the length of each said long pulse is substantially less than the interval between two successive said long pulses.

4. An arrangement as claimed in claim 1, wherein said last-mentioned means includes means for generating saidlong pulses, means for generating said short pulses, and a circuit between said two generating means, said circuit including delaying means for initiating each short pulse under control of the front of a long pulse delayed in said circuit.

5. An arrangement as claimed in claim 4, wherein said delaying means has a delay time substantially equal to wherein is the length of a long pulse and the length of a short pulse.

6. An arrangement as claimed in claim 1, wherein the length of said long pulse and the repetition rate f of said pulses are related by 1 0.5.

7. An arrangement as claimed in claim 1, wherein the length of said long pulse is 3 to 4 times longer than the length of said short pulse.

8. A backward wave oscillator arrangement, comprising means for emitting an electron beam, control means for controlling the emission of said electron beam, means for establishing an electric field in the path traversed by said electron beam, and pulse means for establishing said electric field at a predetermined repetition rate and for simultaneously therewith producing pulses for the control means of said electron beam with the pulses for the control means of said electron beam effectively occurring within the period of and over a substantial portion of the pulses producing said electric field.

9. A backward wave oscillator arrangement according to claim 8, wherein said pulse means includes a first source of pulses, a second source of pulses, and delay means for synchronizing said second source of pulses by said first source of pulses, said first source of pulses establishing said electric field and said second source of pulses producing said pulsed electron beams.

10. In combination with a backward wave oscillator in which an electron beam emitted from cathode means which is adapted to be effectively blocked interacts with a wave travelling in a delay line in a direction opposite to the movement of said electron beam comprising, means for producing unblocking pulses for said electron beam, means for producing pulses to establish an electric field in the interaction space, and means for synchronizing said pulse producing means in such a way that the pulses for unblocking said electron beam occur within the pulses producing said electric field.

References Cited in the file of this patent UNITED STATES PATENTS 2,704,350 Lerbs Mar. 15, 1955 2,824,231 Fernstein et al. Feb. 18, 1958 2,833,956 Reverdin May 6, 1958 OTHER REFERENCES Article: ConcinotronBackward Wave Microwave Oscillator, pages 64-6 6, 157-162 of Tele-Tech. and Electronic Engineering for November 1953.

Article: Raveling-Wave Tubes, pages 23-25, 71 of Radio-Electronic Engineering for April 1954.

Article: Voltage-Tuned Microwave Oscillator, pages 242, 244, 246, 248 and 250 of Electronic for March 1954. 

